Could it have made a hole in a Highlander's sock? (4)

I believe the answer is:

dirk

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'sock?' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for dirk that I've seen before include "Small dagger" , "A short Scottish dagger" , "which might get one stuck in Highlands" , "Highland dagger" , "weapon" .)

I've seen this clue in the Evening Standard.

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